2.8. Fluent Interface

2.8.1. Purpose

To write code that is easy readable just like sentences in a naturallanguage (like English).

2.8.2. Examples

• Doctrine2’s QueryBuilder works something like that example classbelow
• PHPUnit uses fluent interfaces to build mock objects
• Yii Framework: CDbCommand and CActiveRecord use this pattern, too

2.8.3. UML Diagram

2.8.4. Code

You can also find this code on GitHub

Sql.php

<?php
 
namespace DesignPatterns\Structural\FluentInterface;
 
class Sql
{
    /**
     * @var array
     */
    private $fields = [];
 
    /**
     * @var array
     */
    private $from = [];
 
    /**
     * @var array
     */
    private $where = [];
 
    public function select(array $fields): Sql
    {
        $this->fields = $fields;
 
        return $this;
    }
 
    public function from(string $table, string $alias): Sql
    {
        $this->from[] = $table.' AS '.$alias;
 
        return $this;
    }
 
    public function where(string $condition): Sql
    {
        $this->where[] = $condition;
 
        return $this;
    }
 
    public function __toString(): string
    {
        return sprintf(
            'SELECT %s FROM %s WHERE %s',
            join(', ', $this->fields),
            join(', ', $this->from),
            join(' AND ', $this->where)
        );
    }
}

2.8.5. Test

Tests/FluentInterfaceTest.php

<?php
 
namespace DesignPatterns\Structural\FluentInterface\Tests;
 
use DesignPatterns\Structural\FluentInterface\Sql;
use PHPUnit\Framework\TestCase;
 
class FluentInterfaceTest extends TestCase
{
    public function testBuildSQL()
    {
        $query = (new Sql())
                ->select(['foo', 'bar'])
                ->from('foobar', 'f')
                ->where('f.bar = ?');
 
        $this->assertEquals('SELECT foo, bar FROM foobar AS f WHERE f.bar = ?', (string) $query);
    }
}